It has been known heretofore to comminute pigment bars and mix the pulverulent pigment material with plastic pieces being fed to a plastic article forming machine. One such apparatus is disclosed in U.S. Pat. No. 3,811,627 issued May 21, 1974. The patented apparatus includes timer means which controls the period of operation of a rotary cutter thereby determining the relative amount of pigment being mixed with the plastic material to control the depth of color in the finished article. A rotating cutter operates continuously during the reverse cycle of the ram and the rate of feeding pigment to the cutter is controlled by a timer controlling the operation of a plurality of rollers with frictionally engage and advance pigment bars into contact with the rotary cutter. The rollers operate only during a controlled preselected time interval.
In the patented device, to change the relative amount of pigment being added to the plastic, it is necessary to change gear ratios or by changing the length of the time portion cycle. There is no means for instantaneously adjusting said ratio and as a result operation with such prior art apparatus is cumbersome.